Radio access network apparatus and mobile communication system using the same

ABSTRACT

The radio access network for allowing to construct a system abundant in scalability in a W-CDMA mobile communication system. A RNC in the radio access network is physically separated into a C plane control equipment for controlling signaling and a U plane control equipment for processing user data, where the user data is transferred between a mobile terminal and a host device via only the U plane control equipment and a control signal is terminated by the U plane control equipment and the C plane control equipment. This allows a system abundant in scalability to be constructed, and even in the case of soft handover across the C plane control equipments, also enables the continuous use of the same U plane control equipment, thereby eliminating the conventional connection path for connecting between RNCs and preventing delay due to passing through the RNCs.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio access network apparatus and amobile communication system using it, and more particularly to animprovement of a Radio Network Controller (RNC) in a W-CDMA cellularmobile communication system.

2. Description of the Prior Art

An architecture of a W-CDMA communication system that is a mobilecommunication system is shown in FIG. 11. A radio access network (RAN) 1is configured with radio network controllers (RNC) 4, 5 and Nodes B6 to9, and is connected with a core network (CN) 3 as an exchange networkvia an Iu interface. The Nodes B6 to 9 are logical nodes for radiotransmission/reception, and more specifically radio base stationapparatus.

An interface between the Node B and RNC is referred to as Iub, and Iurinterface is also standardized as an interface between RNCs. Each Node Bcovers one or more cells 10 and is connected to a mobile unit (UE) 2 viaa radio interface. The Node B terminates a radio line, and the RNCmanages the Node B and selectively synthesizes radio paths in the caseof soft handover. Note here that the detail of the architecture shown inFIG. 11 is specified in 3GPP (3rd Generation Partnership Projects).

FIG. 12 shows a protocol architecture for the radio interface in theW-CDMA communication system shown in FIG. 11. As shown in FIG. 12, suchprotocol architecture is composed of three protocol layers of a physicallayer (PHY) 11 denoted as L1, data link layers 12 to 14 denoted as L2,and a network layer (RRC: Radio Resource Control) 15 denoted as L3.

The data link layers L2 are separated into three sublayers of a MAC(MediaAccessControl) layer 12, a RLC (RadioLinkControl) layer 13, and aBMC (Broadcast/Multicast Control) layer 14. The MAC layer 12 has aMAC-c/sh (common/share) 121 and a MAC-d (dedicated) 122, and the RLClayer 13 has a plurality of RLCs 131 to 134.

Ellipses in FIG. 12 indicate service access points (SAP) between layersor sublayers, where SAPs between the RLC sublayer 13 and the MACsublayer 12 provide logical channels. That is, the logical channels areprovided from the MAC sublayer 12 to the RLC sublayer 13, and areclassified by functions and logical properties of transmission signalsand characterized by transferred information contents.

The logical channels include a CCCH (Common Control Channel), a PCCH(Paging Control Channel), a BCCH (Broadcast Control Channel), and a CTCH(Common Traffic Channel), for example.

A SAP between the MAC sublayer 12 and the physical layer 11 providestransport channels, which are provided from the physical layer 11 to theMAC sublayer 12. The transport channels are classified by a transmissionform and are characterized depending on how and what information istransmitted via a radio interface.

The transport channels include a PCH (Paging Channel), a DCH (DedicatedChannel), a BCH (Broadcast Channel), and a FACH (Forward AccessChannel), for example.

The physical layer 11 and the sublayers 12 to 14 in the data link layerare controlled by the network layer (RRC) 15 via a C-SAP providing acontrol channel. The detail of the protocol architecture shown in FIG.12 is specified in TR25.925 of 3GPP.

In addition, a C (Control) plane for signaling that transfers a controlsignal and a U (User) plane that transfers user data, are specified inTR 25.925. The the BMC sublayer 14 in L2 is applied only to the U plane.

The RNCs 4, 5 of the radio access network (RAN) 1 in the prior art areapparatus in which both functions of controlling the C plane and U planeare physically integrated.

In a mobile communication system including such a RNC that integrallyhas the control functions of both U plane and C plane, the controlfunction of the C plane is sufficient enough to be added in order toenhance the signaling processing capacity, however, the RNC itself isrequired to be added. Furthermore, although the control function of theU plane is sufficient enough to be added in order to increase thetransfer speed of user data, the RNC itself is required to be added aswell. Therefore, the conventional RNC constitution makes constructing asystem abundant in scalability quite difficult.

Moreover, the following disadvantage arises in soft handover. When a UE(mobile unit) is in a usual setup status, one Radio Link is connectedbetween the RNC and Node B, and when the UE is moved and comes into asoft handover status, two or more paths are connected between the RNCand a plurality of Nodes B. When the UE comes into the soft handoveracross RNCs, a path is connected utilizing an interface referred to asIur (see FIG. 11) between a serving RNC and a drift RNC.

In such a status of soft handover across RNCs, a path for user data maybe connected from one U plane control function unit to a plurality ofNodes B involved in soft handover, however, another path for the userdata needs to be connected between the serving RNC and the drift RNC,wasting resources and causing delay due to passing through the RNCs.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object to provide a radio access network apparatuscapable of constructing a system abundant in scalability and a mobilecommunication system using the same.

Another object of the present invention is to provide a radio accessnetwork apparatus which eliminates waste of resources and prevents delayin the case of soft handover, and a mobile communication system usingthe same.

According to the present invention, the radio access network apparatusis provided between a mobile terminal and a host device having answitching network in the mobile communication system and is connectedwith the mobile terminal via a radio interface. The radio access networkapparatus comprises user plane controlling means for controllingtransfer of user data in relation to the mobile terminal and controlplane controlling means for controlling transfer of signaling having acontrol signal, both of which are physically separated from each other.

The user plane controlling means has a function of terminating a datalink layer of a protocol for the radio interface, and the control planecontrolling means has a function of terminating a network layer of aprotocol for the radio interface. The user data is transferred betweenthe mobile terminal and the host device via the data link layer of theuser plane controlling means, and the signaling is transferred via thedata link layer of the user plane controlling means and the networklayer of the control plane controlling means.

Furthermore, the radio access network apparatus further comprises aradio base station having a function of terminating a physical layer ofa protocol for the radio interface. The user plane controlling meansfurther includes means for selecting data of high receiving quality fromamong the user data coming from a plurality of radio base stationsinvolved in a soft handover state and sending out the selected data tothe host device. Moreover, the user plane controlling means isincorporated into the radio base station. The mobile communicationsystem belongs to a W-CDMA cellular system.

The mobile communication system according to the present inventionincludes the radio access network apparatus described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram according to an embodiment of thepresent invention;

FIG.2 is a diagram illustrating advantages of the embodiment of thepresent invention;

FIG. 3 is a diagram illustrating a status during soft handover when theembodiment of the present invention is employed;

FIG. 4 is a diagram showing a path connection sequence in the case ofsoft handover according to the embodiment of the present invention;

FIG. 5 is a diagram showing the existing (conventional) networkconfiguration and a flow of user data and control signals;

FIG. 6 is a diagram showing a network configuration of IP networkemploying the embodiment of the present invention;

FIG. 7 is a sequence diagram in the case that radio links are setup fora plurality of Nodes B at the same time according to the embodiment ofthe present invention;

FIG. 8 is a sequence diagram when the radio link is additionally setupfor a new Node B according to the embodiment of the present invention;

FIG. 9 is a diagram showing one example of a flow of user data andcontrol signals in the IP network according to the embodiment of thepresent invention;

FIG. 10 is a diagram showing another example of a flow of user data andcontrol signals in the IP network according to the embodiment of thepresent invention;

FIG. 11 is a diagram showing a system architecture in a W-CDMAcommunication system; and

FIG. 12 is a diagram showing the system architecture in FIG. 11 as aprotocol architecture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described below withreference to the drawings. FIG. 1 is a functional block diagram of theembodiment according to the present invention, where the same parts asin FIG. 12 are indicated with the same reference numerals andcharacters. As shown in FIG. 1, a RNC 4 is physically separated into a Cplane control equipment (CPE: Control Plane Equipment) 41 equivalent toa C plane for controlling signaling and a U plane control equipment(UPE: User Plane Equipment) 42 equivalent to a U plane for controllinguser data.

All kinds of signaling between units are communicated directly with acentral control processor (CP: Control Processor) 16 provided in the Cplane control equipment 41. However, RRC signaling between a mobile unit(UE) 2 and the RNC 4 cannot be distinctly separated into the C plane andU plane, so is transferred to a RRC 15 in the C plane control equipment41 after the U plane control equipment 42 terminates RLCs 131 and 132.

In this manner, layers in the existing protocol layer architecture ofthe RNC shown in FIG. 12 are separated into a Node B (radio base stationapparatus) 6 for the physical layer (PHY) 11 denoted as L1, a U planecontrol equipment 42 for the data link layers 12 to 14 denoted as L2,and a C plane control equipment 41 for the network layer 15 and abovedenoted as L3.

The RRC 15 in the C plane control equipment 41 controls each unit forterminating the physical layer 11 in the Node B and a MAC layer 12, aRLC layer 13, and a BMC layer 14 in the U plane control equipment 42, bymeans of C-SAPs (Control Service Access Point) providing controlchannels. Signaling NBAP between the Node B6 and the RNC 4, signalingRNSAP between the RNC 4 and a C plane control equipment (CPE) 43 inanother RNC, and signaling RANAP between the RNC 4 and a MSC (MobileSwitching Center) 31 or an SGSN (Serving GPRS (Global Packet RadioService) Switching Node) 32, are terminated and processed directly bythe CP 16 in the C plane control equipment 41.

Note that the MSC 31 has a circuit switching function and that the SGSN32 has a packet switching function, both of which are included in thecore network (CN) 3 shown in FIG. 11.

The RRC signaling utilized between the RNC 4 and the mobile unit 2 istransferred from the mobile unit 2 via the Node B6 and the MAC layer 12and RLC layer 13 in the U plane control equipment 42, and is terminatedin the RRC layer 15 in the C plane control equipment 41. PCH/FACH isterminated in the MAC-c/sh layer 121 and the RLC layer 13 in the U planecontrol equipment 42 and is transmitted to the C plane control equipment41, since the relation between the Node B6 and the U plane controlequipment 42 is determined after Logical O&M procedure (Logical O&M isthe signaling associated with the control of resources owned by the RNCbut physically implemented in the Node B, and is specified in 3GPPSpecification (25.401)) and is not changed as far as station data is notchanged.

DCH (Dedicated Channel) for transmitting user data allows the connectionbetween the arbitrary Node B and the U plane control equipment 42, andis terminated in the MAC-d layer 122 and the RLC layer 13 to betransmitted to the MSC 31 having a circuit switching function and theSGSN 32 having a packet switching function through the C plane controlequipment 41, after paths between Nodes B are selectively synthesized ina selective synthesis unit 123 of the U plane control equipment 42.

The selective synthesis unit 123 selectively synthesizes DCHs from aplurality of Nodes B in the case of soft handover, and selects a linkhaving the highest link quality (receiving quality) from among theseNodes B.

The apparatus configuration shown in FIG. 1 allows to construct a systemabundant in scalability. That is, only the C plane control equipment 41is added in order to enhance signaling processing capacity, and only theuser plane control equipment 42 is added in order to increase user datatransfer speed. Units in the user plane control equipment 42 have norelation with one another and are controlled by the RRC 15 in the Cplane control equipment 41, which thus enables implementation thereof asa single unit.

FIG. 2 is a diagram showing scalability secured between the C planecontrol equipment (CPE) and the U plane control equipment (UPE)separated from each other according to the embodiment of the presentinvention. The C plane control equipments 41 a to 41 c and the U planecontrol equipments 42 a to 42 c are interconnected via a device 17 suchas an IP router or a hub. The C plane control equipment and the U planecontrol equipment are conventionally integrated as a single RNC unit,therefore the RNC itself is required to be added for extension. However,the C plane control equipment, which performs signaling processing suchas call processing, has the possibility of lacking processing capacitywith increasing call quantity. In this case, by adding a new C planecontrol equipment, processing may easily be dispersed.

For example, in the case that two C plane control equipments 41 a, 41 bare utilized, an algorithm such that the C plane control equipment 41 ais used when a mobile unit has the terminal number whose last one digitis an even number and the C plane control equipment 41 b is used when amobile unit has the terminal number whose last one digit is an oddnumber, is altered by utilizing three C plane control equipments 41 a to41 c into another algorithm such that the C plane control equipment 41 ais used when the last one digit of the terminal number is 0, 1, 2, or 3,the C plane control equipment 41 b is used when the last one digit is 4,5, or 6, and the C plane control equipment 41 c is used when the lastone digit is 7, 8, or 9. This allows easy enhancement of processingcapacity by 1.5 times.

On the other hand, the U plane control equipment, which performstransfer of user data, has the possibility of lacking processingcapacity with increasing quantity of transmitting/receiving data to/fromeach mobile unit. In this case, by adding a new U plane controlequipment, processing may easily be dispersed. For example, theconstitution of connecting three out of Nodes B6 a to 6 f insubordination to each of two U plane control equipments 42 a, 42 b ischanged so as to connect two out of the Nodes B6 a to 6 f insubordination to each of three U plane control equipments 42 a, 42 b,and 42 c, which allows an increase of the transfer speed by 1.5 times.

FIG. 3 is a diagram showing that the terminal UE 2 as a mobile unit isperforming soft handover operation between the Node B6 a and Node B6 b.The DCH is connected to the terminal 2 from both the Nodes B6 a and 6 b.By selective synthesis in the selective synthesis unit 123 of the Uplane control equipment 42 a, a link having higher link quality isselected from the Nodes B6 a and 6 b for transmission to the hostdevice.

FIG. 4 shows a sequence from the state that the terminal UE as a mobileunit is executing voice communication utilizing the Node B#1 (6 a) andthe U plane control equipment (UPE)#1 (42 a) (step S1), going throughthe soft handover requesting between the terminal UE and the Nodes B#2(6 b), to the connection of a path between the terminal UE and the NodeB#2. The C plane control equipment (CPE)#1 (41 a) manages resources ofthe U plane control equipment #1 and the Node B#1, and the C planecontrol equipment #2 (41 b) manages resources of the U plane controlequipment #2 (42 b) and the Node B#2.

A soft handover request is notified as “MESUREMENT REPORT (RRC)” fromthe terminal UE to the C plane control equipment #1 via the Node B#1 andthe U plane control equipment #1 (step S2). The C plane controlequipment #1 obtains an IP address for soft handover in regard to the Uplane control equipment #1 and notifies the U plane control equipment #1of the IP address together with “RADIO LINK SETUP REQUEST” (step S3).The U plane control equipment #1 responds to the C plane controlequipment #1 by “RADIO LINK SETUP RESPONSE” (step S4).

Next, the C plane control equipment #1 transmits the IP address of the Uplane control equipment #1 obtained for soft handover together with“RADIO LINK SETUP REQUEST (RNSAP)” to the C plane control equipment #2managing the Node B#2 as a moving destination (step S5). The C planecontrol equipment #2 transmits the IP address of the U plane controlequipment #1 obtained for soft handover together with “RADIO LINK SETUPREQUEST (NBAP)” to the Node B#2 (step S6).

The Node B#2 notifies the C plane control equipment #2 of an IP addressof the Nodes B#2 together with “RADIO LINK SETUP RESPONSE (NBAP)” (stepS7). Next, the C plane control equipment #2 notifies the C plane controlequipment #1 of the IP address of the Node B#2 together with “RADIO LINKSETUP RESPONSE (RNSAP)” (step S8). The C plane control equipment #1notifies the U plane control equipment #1 of the IP address of the NodeB#2 by “RADIO LINK SETUP INDICATION” (step S9).

By these procedures, the IP address of the Node B#2 is notified to the Uplane control equipment #1, and the IP address of the U plane controlequipment #1 is notified to the Node B#2, thereby allowing thetransmission/reception of user data. At the same time, the C planecontrol equipment #1 notifies the terminal UE of “ACTIVE SET UPDATE(RRC) (step S10). Then, the terminal UE notifies the C plane controlequipment #1 of “ACTIVE SET UPDATE COMPLETE (RRC)” (step S11) afterwhich radio synchronization is started between the terminal UE and theNode B#2 (step 12).

After the layer 1 (L1) synchronization for the radio line between theterminal UE and the Node B#2 is completed, “RADIO LINK RESTOREINDICATION (NBAP)” is notified from the Node B#2 to the C plane controlequipment #2 (step S13). The C plane control equipment #2 transmits“RADIO LINK RESTORE INDICATION (RNSAP)” to the C plane control equipment#1 (step S14), after which the path is completely established betweenthe terminal UE and the Node B#2. Consequently, paths for soft handoverconnected to one U plane control equipment #1 from the Nodes B#1 and #2are established (step S15).

Thus, in the case of soft handover across RNCs, by connecting paths fromone U plane control equipment to a plurality of Nodes B withoutestablishing a path between a drift RNC and a serving RNC for user data,soft handover may be achieved, which enables the continuous use of thesame U plane control equipment and thus eliminates the path betweenRNCs, thereby leading to effective utilization of resources andpreventing delay due to passing through the RNCs.

Next, a conceivable modification is such that the RNC is separated intothe C plane control equipment and the U plane control equipment and thatthe U plane control equipment is incorporated into the Node B. In thiscase, if the U plane control equipment incorporated into the Node B doesnot have the function of selectively synthesizing user data (theselective synthesis unit 123 in FIG. 1), soft handover via a pluralityof Nodes B is not executable. This means unenjoyment of merits ofutilizing CDMA within radio zones. It is thus conceivable to provideeach Node B with the function of selectively synthesizing user data torealize communication between Nodes B.

FIG. 5 shows the conventional network configuration and a flow of userdata and control signals. In this network configuration, when softhandover is performed involving plural Nodes B6 a to 6 c, an SRNC(Serving RNC) 4 a terminates user data and control signals. When softhandover is performed involving plural RNCs, user data and controlsignals are transferred from the SRNC 4 a to a DRNC (Drift RNC) 4 b viaan interface Iur.

FIG. 6 shows a network configuration in the case that the RNC isseparated into the C plane control equipment 41 and the U plane controlequipment 42 and that the U plane control equipments 42 a to 42 c areincorporated into the Nodes B6 a to 6 c, respectively. The Nodes B6 a to6 c, the C plane control equipment 41, the CN 3 are connected with oneanother via an IP network 100.

Next, shown is how soft handover involving plural Nodes B is executed inthe IP network shown in FIG. 6. It is assumed here that the C planecontrol equipment 41 is notified IP addresses of the Nodes B.

FIG. 7 shows an example of setting a radio link (RL) via two Nodes Bfrom a state in which the terminal UE has no radio link (RL). The Cplane control equipment (CPE) selects a Node B (Node B#1 in FIG. 7) as aserving Node from among a plurality of Nodes B (Node B#1 and Node B#2 inFIG. 7) (step S20). The C plane control equipment notifies both theNodes B of an IP address of the serving Node B (Node B#1 in FIG. 7) andan IP address of the other Node B (Node #2 in FIG. 7) so as to indicatethe difference of the IP addresses therebetween by means of “RADIO LINKSETUP REQUEST” massage (steps S21 and S22).

The C plane control equipment designates a Node B controlling cells ofthe highest quality as a serving Node B. Both the Nodes B compare theirown IP addresses to the IP address of the serving Node B, and when suchown IP address is the same as that of the serving Node B, the Node Bhaving the same IP address recognizes itself as the serving Node B (stepS22). Nodes B other than that recognize the IP address of the servingNode B as a transfer destination for UL (Up Link) data (step S24).

Each Node B secures resources necessary for setting up a radio link, andthen returns “RADIO LINK SETUP RESPONSE” message to the C plane controlequipment (steps S25 and S26), thereafter establishing thesynchronization of the U plane (step S27).

In the case of DL (Down Link) data transfer (step S28), the serving NodeB transfers data to the IP address of the other Node B notified in the“RADIO LINK SETUP REQUEST” massage (step S29). In the case of UP (UpLink) data transfer, the serving Node B compares data received from eachNode B with one another and transfers data of the highest quality to thehost (step S30).

FIG. 8 shows an example from a state that the mobile unit already has aradio link to a state that the mobile unit comes into soft handovercondition by adding a radio link via a new Node B. In this case, theNode B having a radio link already set up (Node B#2 in FIG. 8) (stepS31) needs to be notified of an IP address of a serving Node B and IPaddresses of Nodes B involved in soft handover.

First, a radio link is setup (step S34) for a new Node B (Node B#1 inFIG. 8) by means of “RADIO LINK SETUP REQUEST” massage (step S32) and“RADIO LINK SETUP RESPONSE” message (step S33), and then all the Nodes Binvolved in soft handover are notified of the IP address of the servingNode B and IP addresses of Nodes B involved in soft handover.

As means for the above, a new massage of “SOFT HANDOVER INDICATION”should be proposed (steps S36 and S37). This massage includes the IPaddress of the serving Node B and IP addresses of Nodes B involved insoft handover. Operations thereafter is the same as those in FIG. 7, soare indicated with the same reference numerals and characters.

FIGS. 7 and 8 show examples of soft handover involving two Nodes B,however, two or more Nodes B involved in soft handover are alsoapplicable to the above mechanism. In this case, plural IP addresses areset as “OTHER NODE B IP ADDRESS” in steps 21 and 22 of FIG. 7 and insteps 36 and 37 of FIG. 8.

FIG. 9 shows a flow of user data and control signals in the IP network100. FIG. 9 corresponds to the sequences in FIGS. 7 and 8.

The example of providing selective synthesis function to each Node B isdescribed above, although such installation of the selective synthesisfunction to the Node B raises a problem of increasing the productioncost of the Node B. To solve the problem, it is conceivable to providethe selective synthesis function to only one Node B out of plural NodesB. In this case, user data is terminated in the Node B having suchselective synthesis function at the time of soft handover via pluralNodes B. This may result in maintained soft handover function which isan advantageous feature of CDMA.

FIG. 10 shows a flow of user data and control signals in the IP network100 in the case that the Node B#1 and the Node B#2 are involved in softhandover but neither of them has the selective synthesis function. InFIG. 10, a Node B#3 (6 c) has the selective synthesis function.

To realize such processing, the CN 3 is necessary to have IP addresses,locations, the presence of the selective synthesis function, loadstatus, and the like, of all Nodes B within the IP network 100. In theexample of FIG. 10, the CN 3 notifies the Nodes B#1 and #2 of an IPaddress of a serving Node B, and the Nodes B#1 and #2 transfer data tothe serving Node B. The CN 3 also instructs the Nodes B#3 to function asa serving.

When selecting the serving Node B from Nodes B other than those involvedin soft handover, the CN 3 takes account of physical distances betweenthe Nodes B involved in soft handover and the Node B working as theserving Node, and load status of the Nodes B targeted for the serving.

As described in the above, according to the present invention, a RNC isphysically separated into a C plane control equipment as a signalingcontrol unit and a U plane control equipment as a user data processingunit, thus allowing a system abundant in scalability to effectively beconstructed. In addition, each unit in the U plane control equipment hasno relation with one another, enabling separate installation.

Furthermore, even in the case of soft handover across the C planecontrol equipments, the same U plane control equipment may becontinuously utilized, which eliminates the conventional path betweenRNCs and thus effectively prevents delay due to passing through theRNCs.

Moreover, even in the case that the Node B has the function ofterminating user data which is performed in the present RNC and thatsuch Node B is connected to an IP network, by providing a selectivesynthesis function for user data to a predetermined Node B, softhandover involving a plurality of Nodes B may effectively be achieved.

1. A radio access network apparatus provided between a mobile terminaland a host device having an switching network in a mobile communicationsystem and connected to the mobile terminal via a radio interface, theradio access network apparatus comprising: user plane controlling meansfor controlling transfer of user data in relation to the mobileterminal; control plane controlling means for controlling transfer ofsignaling having a control signal, wherein the user plane controllingmeans and the control plane controlling means are physically separatedfrom each other, and wherein the user plane controlling means isincorporated into the radio base station; and wherein the user planecontrolling means has a function of terminating a data link layer of aprotocol of the radio interface, and the control plane controlling meanshas a function of terminating a network layer of a protocol of the radiointerface.
 2. The radio access network apparatus according to claim 1,wherein the user data is transferred between the mobile terminal and thehost device via the data link layer of the user plane controlling means,and the signaling is transferred via the data link layer of the userplane controlling means and the network layer of the control planecontrolling means.
 3. The radio access network apparatus according toclaim 1 further comprising: a radio base station having a function ofterminating a physical layer of a protocol of the radio interface. 4.The radio access network apparatus according to claim 3, wherein theuser plane controlling means further includes means for selecting dataof high receiving quality from among the user data coming from aplurality of the radio base stations involved in soft handover state andsending out the selected data to the host device.
 5. The radio accessnetwork apparatus according to claim 1, wherein the mobile communicationsystem is a W-CDMA cellular system.
 6. A mobile communication systemincluding a mobile terminal, a host device having an exchange network,and a radio access network apparatus provided between the mobileterminal and the host device and connected to the mobile terminal via aradio interface, wherein the radio access network apparatus comprises:user plane controlling means for controlling transfer of user data inrelation to the mobile terminal, and control plane controlling means forcontrolling transfer of signaling having a control signal, the userplane controlling means and the control plane controlling means beingphysically separated from each other, and wherein the user planecontrolling means is incorporated into the radio base stations; andwherein the user plane controlling means has a function of terminating adata link layer of a protocol of the radio interface, and the controlplane controlling means has a function of terminating a network layer ofa protocol of the radio interface.
 7. The mobile communication systemaccording to claim 6, wherein the user data is transferred in acontrolled manner between the mobile terminal and the host device viathe data link layer of the user plane controlling means, and thesignaling is transferred in a controlled manner via the data link layerof the user plane controlling means and the network layer of the controlplane controlling means.
 8. The mobile communication system according toclaim 6, wherein the radio access network apparatus further comprises aradio base station having a function of terminating a physical layerhaving a protocol of the radio interface.
 9. The mobile communicationsystem according to claim 8, wherein the user plane controlling meansfurther includes means for selecting data of high receiving quality fromamong the user data coming from a plurality of the radio base stationsinvolved in soft handover state and sending out the selected data to thehost device.
 10. The mobile communication system according to claim 6,which is a W-CDMA cellular system.